Refactor Stats to typed keys and fix peak-tracking race

Replace the map-backed Stats counter with a fixed [numStats]int array
indexed by a new StatKey enum, eliminating the hand-maintained map
initialization and the parallel string-keyed Values() map.

Fix a check-then-act race in the connection peak tracking: the old
Get-then-Set across two lock acquisitions could let concurrent
connections clobber each other's update. The new atomic Max method does
the compare-and-set under a single lock.

Values() now returns a typed StatValues struct whose JSON tags preserve
the existing /api/v1/stats wire format.

1 files changed, 2 insertions, 4 deletions

diff --git a/hotline/server.go b/hotline/server.go
index dcb90e7..d757062 100644
--- a/hotline/server.go
+++ b/hotline/server.go
@@ -157,7 +157,7 @@ func NewServer(options ...Option) (*Server, error) {
 	return &server, nil
 }
 
-func (s *Server) CurrentStats() map[string]interface{} {
+func (s *Server) CurrentStats() StatValues {
 	return s.Stats.Values()
 }
 
@@ -648,9 +648,7 @@ func (s *Server) handleNewConnection(ctx context.Context, rwc io.ReadWriteCloser
 	c.Server.Stats.Increment(StatConnectionCounter, StatCurrentlyConnected)
 	defer c.Server.Stats.Decrement(StatCurrentlyConnected)
 
-	if len(s.ClientMgr.List()) > c.Server.Stats.Get(StatConnectionPeak) {
-		c.Server.Stats.Set(StatConnectionPeak, len(s.ClientMgr.List()))
-	}
+	c.Server.Stats.Max(StatConnectionPeak, len(s.ClientMgr.List()))
 
 	// Scan for new transactions and handle them as they come in.
 	for scanner.Scan() {